atm: Revert atm_account_tx() if copy_from_iter_full() fails.

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: atm: Revert atm_account_tx() if copy_from_iter_full() fails. In vcc_sendmsg(), we account skb->truesize to sk->sk_wmem_alloc by atm_account_tx(). It is expected to be reverted by atm_pop_raw() later called by vcc->dev->ops->send(vcc, skb). However, vcc_sendmsg() misses the same revert when copy_from_iter_full() fails, and then we will leak a socket. Let's factorise the revert part as atm_return_tx() and call it in the failure path. Note that the corresponding sk_wmem_alloc operation can be found in alloc_tx() as of the blamed commit. $ git blame -L:alloc_tx net/atm/common.c c55fa3cccbc2c~

References

• https://git.kernel.org/stable/c/5e0d00992118e234ebf29d5145c1cc920342777e
• https://git.kernel.org/stable/c/c12430edd92fd49a4800b0f3fb395b50cb16bcc1
• https://git.kernel.org/stable/c/287b4f085d2ca3375cf1ee672af27410c64777e8
• https://git.kernel.org/stable/c/2252c539c43f9a1431a7e8b34e3c18e9dd77a96d
• https://git.kernel.org/stable/c/3902205eadf35db59dbc2186c2a98b9e6182efa5
• https://git.kernel.org/stable/c/3d828519bd69bfcaabdd942a872679617ef06739
• https://git.kernel.org/stable/c/7d6bc28cfe5c8e3a279b4b4bdeed6698b2702685
• https://git.kernel.org/stable/c/7851263998d4269125fd6cb3fdbfc7c6db853859